Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/soft gamma ray sky using the Earth occultation technique (EOT). Each time a source in our catalog is occulted ...by (or exits occultation by) the Earth, we measure its flux using the change in count rates due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors for daily monitoring. Light curves, updated daily, are available on our website http://heastro.phys.lsu.edu/gbm. Our software is also capable of performing the Earth occultation monitoring using up to 128 energy bands, or any combination of those bands, using our 128-channel, 4-s CSPEC data. The GBM BGO detectors, sensitive from about 200 keV to 40 keV, can also be used with this technique. In our standard application of the EOT, we use a catalog of sources to drive the measurements. To ensure that our catalog is complete, our team has developed an Earth occultation imaging method. In this talk, I will describe both techniques and the current data products available. I will highlight recent and important results from the GBM EOT, including the current status of our observations of hard X-ray variations in the Crab Nebula.
GRB 221009A, The BOAT Burns, Eric; Svinkin, Dmitry; Fenimore, Edward ...
arXiv (Cornell University),
03/2024
Paper, Journal Article
Odprti dostop
GRB 221009A has been referred to as the Brightest Of All Time (the BOAT). We investigate the veracity of this statement by comparing it with a half century of prompt gamma-ray burst observations. ...This burst is the brightest ever detected by the measures of peak flux and fluence. Unexpectedly, GRB 221009A has the highest isotropic-equivalent total energy ever identified, while the peak luminosity is at the \(\sim99\)th percentile of the known distribution. We explore how such a burst can be powered and discuss potential implications for ultra-long and high-redshift gamma-ray bursts. By geometric extrapolation of the total fluence and peak flux distributions GRB 221009A appears to be a once in 10,000 year event. Thus, while it almost certainly not the BOAT over all of cosmic history, it may be the brightest gamma-ray burst since human civilization began.
GW230529 is the first compact binary coalescence detected by the
LIGO-Virgo-KAGRA collaboration with at least one component mass confidently in
the lower mass-gap, corresponding to the range ...3-5$M_{\odot}$. If interpreted
as a neutron star-black hole merger, this event has the most symmetric mass
ratio detected so far and therefore has a relatively high probability of
producing electromagnetic (EM) emission. However, no EM counterpart has been
reported. At the merger time $t_0$, Swift-BAT and Fermi-GBM together covered
100$\%$ of the sky. Performing a targeted search in a time window $t_0-20
\text{s},t_0+20 \text{s}$, we report no detection by the Swift-BAT and the
Fermi-GBM instruments. Combining the position-dependent $\gamma-$ray flux upper
limits and the gravitational-wave posterior distribution of luminosity
distance, sky localization and inclination angle of the binary, we derive
constraints on the characteristic luminosity and structure of the jet possibly
launched during the merger. Assuming a top-hat jet structure, we exclude at
90$\%$ credibility the presence of a jet which has at the same time an on-axis
isotropic luminosity $\gtrsim 10^{48}$ erg s$^{-1}$, in the bolometric band 1
keV-10 MeV, and a jet opening angle $\gtrsim 15$ deg. Similar constraints are
derived testing other assumptions about the jet structure profile. Excluding
GRB 170817A, the luminosity upper limits derived here are below the luminosity
of any GRB observed so far.
Monitoring the Crab Nebula with LOFT Wilson-Hodge, Colleen A
NASA Center for AeroSpace Information (CASI). Conference Proceedings,
09/2012
Conference Proceeding
From 2008-2010, the Crab Nebula was found to decline by 7% in the 15-50 keV band, consistently in Fermi GBM, INTEGRAL IBIS, SPI, and JEMX, RXTE PCA, and Swift BAT. From 2001-2010, the 15-50 keV flux ...from the Crab Nebula typically varied by about 3.5% per year. Analysis of RXTE PCA data suggests possible spectral variations correlated with the flux variations. I will present estimates of the LOFT sensitivity to these variations. Prior to 2001 and since 2010, the observed flux variations have been much smaller. Monitoring the Crab with the LOFT WFM and LAD will provide precise measurements of flux variations in the Crab Nebula if it undergoes a similarly active episode.
